Due to the limitation of the number of bit rates for encoding speech signals and the influence of human auditory characteristics, low-frequency band information in a speech signal is always encoded first in an audio encoding algorithm. Compared with narrow-band speech, wide-band speech has the characteristics of being fuller and more natural; therefore, the acoustic quality can be improved by increasing the bandwidth for transmitting speech signals. When the number of bit rates for encoding speech signals is small, a bandwidth extension technology can be adopted to extend the bandwidth range of the speech signals and improve the quality of the speech signals.
In recent years, the bandwidth extension technology has developed significantly, and has found commercial applications in several fields, including acoustic enhancement of bass loudspeakers and high frequency enhancement of coded voice and audio.
Among current bandwidth extension methods, the encoding technology of low-frequency band information adopts existing encoding and decoding algorithms; and during the process of encoding and decoding high-frequency band information, a small number of bits are generally adopted to encode the high-frequency band information, and the high-frequency band information is recovered at a decoding end by using the correlation between the high-frequency and low-frequency bands.
In the implementation of the present invention, the inventor finds that a transient signal has the following characteristics different from those of a non-transient signal: in the time domain, the signal energy of the transient signal has a large instant change; while in the frequency domain, the frequency spectrum of the transient signal is smooth. In the prior art, the time envelope of the transient signal is not modified, and due to the influence of the processing in the signal encoding process, such as process by frame by frame, time-frequency transform, and frequency envelope, the transient signal is likely to generate a pre-echo; therefore, the prior art has the disadvantage that the effect of the transient signal recovered at the decoding end is not satisfactory.